Layered stack for transparent substrates

ABSTRACT

A layer stack for the surface coating of transparent substrates, in particular panes of glass, has at least one metal oxide composite layer produced by reactive cathodic sputtering and contains Zn oxide and Sn oxide. Relative to the total amount of metal, this metal oxide composite layer contains from 0.5 to 6.5% by weight of one or more of the elements Al, Ga, In, B, Y, La, Ge, Si, P, As, Sb, Bi, Ce, Ti, Zr, Nb and Ta. In a layer stack which has a silver layer as a functional layer, the metal oxide composite layer may be used as an upper and/or lower antireflection layer, as a diffusion barrier layer, as a sublayer of an antireflection layer and/or as an upper cover layer.

BACKGROUND OF THE INVENTION

The invention relates to a layer stack for transparent substrates, inparticular for panes of glass, with at least one metal oxide compositelayer produced notably by reactive cathodic sputtering from a metallicalloy target containing Zn and Sn. The substrates on which the layersare deposited may also be made of transparent organic polymers, and maybe rigid or flexible. Rigid polymeric substrates may be chosen in thefamily of polycarbonates or among certains polyurethans. They may be inmethylmetacrylate PMMA. Fexible substrates may be chosen for example inpolyethyle terephtalate PET, a film which is afterwards laminated withtwo thermoplastic sheets (in polyvinyl butyral PVB for example) betweentwo gass panes.

The patent applications EP 0183 052 and EP 0226 993 disclosehigh-transparency low-E layer stacks in which a metallic functionallayer, in particular a thin silver layer, is embedded between twodielectric antireflection layers which are the oxidation product of azinc/tin alloy. These dielectric oxide layers are sputtered using themethod of magnetic field-enhanced reactive cathodic sputtering with anoxygen-containing working gas from a metallic target which consists of aZn/Sn alloy. Depending on the Zn:Sn ratio, the oxide composite layerproduced in this way will contain a greater or lesser amount of zincstannate Zn₂SnO₄, which gives the layer particularly favourableproperties especially in terms of mechanical and chemical stability.Zn:Sn alloys with a Zn:Sn ratio of from 46:54 to 50:50% by weight arepreferably used as the target.

In the technical sputter process with industrial coating stacks, thesputtering of Zn₂SnO₄ layers from Zn/Sn alloy targets is more difficultthan the sputtering of pure ZnO or SnO₂ layers. This is because,particularly at the start of the sputtering process, the material on thetarget and on parts of the sputter chamber lead to insulation effects,the consequences of which are defective products and thereforeproduction rejects. Furthermore, alloy targets of this type must beoperated with reduced sputtering rates, that is to say with reducedelectrical power, because the target alloy has a lower meltingtemperature than the melting temperatures of the two components,especially in the region of the eutectic composition. The cooling oftargets of this type must therefore be particularly intense. This can inturn be achieved only with targets of particular design, the productionof which is comparatively expensive.

SUMMARY OF THE INVENTION

The object of the invention is, on the one hand, further to improve themechanical and chemical properties of dielectric layers containing zincstannate and, on the other hand, to reduce the difficulties which occurduring the process of sputtering Zn/Sn alloys.

According to the invention, this object is achieved in that the metaloxide composite layer contains one or more of the elements Al, Ga, In,B, Y, La, Ge, Si, P, As, Sb, Bi, Ce, Ti, Zr, Nb and Ta.

It has been shown that, by the addition according to the invention ofthe said elements, which without exception are among the elements inmain and subgroups III, IV and V of the Periodic Table, a considerableimprovement is obtained in all the important layer properties, with animprovement in the efficiency during the sputter process as well.

DETAILED DESCRIPTION OF THE INVENTION

The mixed oxides created by the elements added according to theinvention, for example by the addition of Al and Sb, have thequalitative composition ZnO.ZnSnO₃.Zn₂SnO₄.ZnAl₂O₄.ZnSb₂O₆ depending onthe choice of the amounts of the metals Zn and Sn. On crystallization,some of these oxides form spinel structures, which per se crystallizewith particularly dense atomic ordering. The improvements obtained inthe layer properties can probably be explained by the particularly highpacking density obtained for the spinel structures by the incorporationof the said added elements, while the favourable effect during thesputter process is probably attributable to the increase in theelectrical conductivity of the mixed oxides which is obtained by theincorporation of the added elements. Owing to the dense crystalstructure, the layers not only have particularly high mechanical andchemical stability, but also hinder diffusion processes into this layeror through this layer. This reduces the risk of the onset ofmodifications in the said layer or in any other layer of the stack whichmay be attributable to water molecules and oxygen and Na⁺ and, whereapplicable (ie when the stack contains Ag layer(s)), Ag⁺ diffusing in,especially during heat-treatment and storage processes.

For a maximally dense spinel structure, it is particularly favourable ifthe ionic radius of the added element is not too different from theionic radius of Zn²⁺ and Sn⁴⁺, which have ionic radii of 0.83 angstrom(Zn²⁺) and 0.74 angstrom (Sn⁴⁺), respectively. This condition issatisfied, in particular, for the elements Al and Sb, with which theionic radius of Al³⁺=0.57 Å, and of Sb⁵⁺=0.62 Å. On the other hand, asalready mentioned, the incorporation of the said added elements into theat least partially crystallized layer increases the electricalconductivity of the oxide build-ups on the anode faces and walls of thecoating chambers, as well as on the target surface itself. As a result,the operating times of the target during the sputter process are in turnimproved considerably, so that not only an improvement in the layerproperties, but also an improvement in the sputter process can beobserved.

The amount of added elements according to the invention in the metaloxide composite layer is preferably from 0.5 to 6.5% by weight relativeto the total amount of metal.

Compositions of the metal oxide composite layer which have been found tobe particularly advantageous are those in which, in each case relativeto the total amount of metal, the amount of Zn is from 35 to 70% byweight and the amount of Sn is from 29 to 64.5% by weight. For theproduction of this metal oxide composite layer, alloy targets havingfrom 50 to 70%, notably 66 to 69% by weight Zn, from 29 to 50%, notably29 to 32% by weight Sn and from 1 to 40% by weight Al or Sb (notably 1.5to 30%) are preferably employed.

The metal composite layers according to the invention can in particularbe used successfully in partially reflecting layer stacks with ametallic functional layer made of silver. In such layer stacks, they canbe used both as a bonding or antireflection layer, as a condensationlayer for silver layers deposited on top, as a blocker layer below orabove the silver layers and as a sublayer in the region of the bottomand/or top layer of the layer stack.

Illustrative embodiments for layer stacks according to the inventionwill be described below, the properties respectively achieved beingcompared with the properties of a corresponding layer stack according tothe prior art.

In order to assess the layer properties, ten different tests werecarried out on all the samples, namely:

A Cracking hardness

In this case, a weighted needle is drawn over the layer at a definedspeed. The weight under which traces of cracking can be seen is used asthe measure of the cracking hardness.

B Cracking hardness after storage in water

Test procedure as in A, but after storing the samples in water at 20° C.for 30 min.

C Erichsen wash test according to ASTM 2486

Visual assessment

D Water condensation test (WCT)

The samples are exposed for 140 h to a temperature of 60° C. at 1000%relative humidity. Visual assessment.

E Zn²⁺ leaching

The measurement is taken using the plate method according to Kimmel etal., Z. Glastechnische Berichte 59 (1986) p. 252 et seq. The test givesinformation about the hydrolytic resistance of layer stacks containingZn.

F Ag⁺ leaching

The measurement is again taken using the plate method according toKimmel et al. used to determine the Zn²⁺ leaching. The result of themeasurement gives an analytical gauge of the density of the dielectriclayers over the Ag layer.

G Hydrochloric acid test

In this case, the glass sample is dipped for 8 min in 0.01 n HCl at 38°C. and the % emissivity loss is established.

H Hydrochloric acid test, visual assessment

The glass sample is dipped as for G in hydrochloric acid. The assessmentcriterion used is what can be seen on the edge which is immersed.

I EMK Test

This test is described in Z. Silikattechnik 32 (1981) p. 216“Untersuchungen zur elektrochemischen Prüfung dünner Metallschichten”[Studies of the electrochemical testing of thin metal layers]. It givesinformation about the passivating quality of the cover layer above thesilver layer, and about the corrosion resistance of the Ag layer. Thelower the potential difference (in mV) between the layer stack and thereference electrode, the better the layer quality.

K Water film test

The layer side of the samples is brought into contact for 24 h with athin film of water. The test gives information about the storagestability of coated panes of glass stacked in a pile if traces of waterenter between the panes of glass. The assessment is made visually.

COMPARATIVE EXAMPLE 1

In an industrial continuous magnetron stack, a layer stack according tothe prior art, with the following layer sequence, was applied undercustomary coating conditions to 6 mm thick panes of float glass:

glass pane-40 nm SnO₂-2 nm CrNi-10 nm Ag-4 nm CrNi-37 nm SnO₂-3 nmZn₂SnO₄.

The CrNi layers were sputtered from a target made of a CrNi alloy with20% by weight Cr and 80% by weight Ni in an Ar atmosphere, while theZn₂SnO₄ layer was reactively sputtered in an Ar/O₂ atmosphere from atarget made of a Zn/Sn alloy with 52.4% by weight Zn and 47.6% by weightSn.

During the deposition of the Zn₂SnO₄ layer, undesired electric arcsoccurred at the start of the sputtering process, and these led tocoating defects. Furthermore, impressions of the suckers used in thedevices for stacking the panes of glass could be seen on the coatedpanes of glass.

The tests referred to under A to K were carried out on correspondingsamples of the coated panes of glass. The results of the tests arecollated in Table 1, together with the results of the tests carried outon corresponding illustrative embodiment 1.

ILLUSTRATIVE EMBODIMENT 1

In the same coating stack, and under the same coating conditions, alayer stack according to the invention, with the following layersequence, was applied to 6 mm thick panes of float glass:

Glass-40 nm SnO₂-2 nm CrNi-10 nm Ag-4 nm CrNi -37 nm SnO₂ -3 nmZn_(x)Sn_(y)Al_(z)O_(n).

The only difference from comparative example 1 consisted in the factthat the top cover layer of the layer stack was reactively sputteredfrom a target which consisted of an alloy having 68% by weight Zn, 30%by weight Sn and 2% by weight Al. During the sputtering of this topcover layer, no undesired electric arcs were observed. Furthermore, itwas unexpectedly found that no undesired sucker impressions could beseen with this layer stack.

The test results obtained with this layer stack are given in Table 1below:

TABLE 1 Comparative Illustrative Test example 1 embodiment 1 A (g) 33 35B (g) 35 55 C (1000 strokes) 1 medium, several 1 small crack smallcracks D pronounced reddening very slight reddening E (mg/25 ml)  0.19 0.19 F (mg/25 ml)  0.47  0.03 G (ΔE in %)  1  0 H red streaks nodefects I (mV) 95.5 86 K no defects no defects

It can be seen from Table 1 that the layer stack according to theinvention gives better results in almost all the tests than the layerstack according to the comparative example.

COMPARATIVE EXAMPLE 2

In the same coating stack, under comparable coating conditions, thefollowing layer stack according to the prior art was again applied to 6mm thick panes of float glass:

Glass pane-40 nm SnO₂-2 nm CrNi-10 nm Ag-4 nm CrNi-34 nm SnO₂-4 nmZn₂SnO₄-4.5 nm TiO₂.

The Zn₂SnO₄ layer was again reactively sputtered from a metallic alloytarget which consisted of 52.4% by weight Zn and 47.6% by weight Sn.During the sputtering of the Zn₂SnO₄ layer, undesired arcs were againobserved, and these led to coating defects. The TiO₂ layer wasreactively sputtered from a metallic titanium target with a DMS cathodeand a working gas composed of an Ar/O₂/N₂ mixture.

The tests referred to under A to K were again carried out on samples ofthe coated panes of glass. The results are collated in Table 2, togetherwith the test results found with the samples produced according toillustrative embodiment 2.

ILLUSTRATIVE EMBODIMENT 2

Under the same coating conditions, with the same coating stack, a layerstack according to the invention with the following layer sequence wasapplied with the same coating stack to 6 mm thick panes of float glass:

Glass-40 nm SnO₂-2 nm CrNi-10 nm Ag-4 nm CrNi-34 nm SnO₂-4 nmZn_(x)Sn_(y)Sb_(z)O_(n)-4.5 nm TiO₂.

The only difference from the comparative example consisted in the factthat, in order to produce the sublayer containing the Zn/Sn mixed oxide,the target used was made of an alloy consisting of 68% by weight Zn, 30%by weight Sn and 2% by weight Sb. No undesired arcs were observed duringthe sputtering of this alloy.

Samples of the coated panes of glass were subjected to the testsreferred to under A to K. The results are collated in Table 2 below,together with the results obtained with the samples of comparativeexample 2.

TABLE 2 Comparative Illustrative Test example 2 embodiment 2 A (g) 3045-50 B (g) 35 55 C (1000 strokes)  1 medium crack  1 small crack D  140 hours weak reddening still no defects after 400 h E (mg/25 ml) 0.19  0.15 F (mg/25 ml)  0.35  0.01 G (ΔE in %)  1  0 H red streaks nodefects I (mV) 80 30 K no defects no defects

The test results show that the TiO₂ cover layer has better compatibilitywith the composition layer according to the invention than with the zincstannate layer of the comparative example. This is manifested by afurther improvement in the test results, in particular in thesubstantially better results in test D (water condensation test) and ina significant improvement to the EMF test result. The result of the Ag*leaching is also substantially better, and this layer stack thus hasoutstanding quality overall.

COMPARATIVE EXAMPLE 3

In the same coating stack, the following layer stack was once moreapplied under comparable coating conditions to 6 mm thick panes of floatglass as comparative samples:

Glass-20 nm SnO₂-17 nm ZnO-11 nm Ag-4 nm TiO₂-40 nm SnO₂.

This layer stack is a tried and tested layer stack according to theprior art.

The tests referred to under A to K were also carried out on samples ofthe panes of glass coated with this layer stack. The test results areonce more collated in Table 3 together with the test results found withsamples produced according to illustrative embodiment 3.

ILLUSTRATIVE EMBODIMENT 3

Under coating conditions comparable with those in comparative example 3,a layer stack according to the invention with the following layersequence was applied with the same coating stack to 6 mm thick panes offloat glass:

Glass-20 nm SnO₂-17 nm ZnO-11 nm Ag-1 nm Ti-3 nmZn_(x)Sn_(y)Al_(z)O_(n)-40 nm SnO₂.

In this case, the metal oxide composite layer according to the inventionthus serves together with the very thin Ti layer arranged directly onthe silver layer as a blocker layer.

The results of the tests carried out on corresponding samples arelikewise reported in Table 3.

TABLE 3 Comparative Illustrative Test example 3 embodiment 3 A (g)  4.5 7.5 B (g)  4.5  8 C (350 strokes)  2 small scratches no scratches D  70 hours red spots no defects E (mg/25 ml)  0.80  0.30 F (mg/25 ml) 0.60  0.20 G (ΔE in %)  8  1 H red streaks no defects I (mV) 210 130 Kno defects no defects

Comparing the test results shows that considerable improvements are alsoobserved in both the chemical and the mechanical properties in the casewhen the layer according to the invention is used as a blocker layer.

As a conclusion, the composite layers according to the invention make itpossible both to simplify the deposition process and to increase thechemical and mechanical durability of the stacks which incorporate them,especially when the layer of the invention are the last or just belowthe last layer of the stack (the outermost one). This kind of layermakes it possible to render more resistant stacks of layers using asdielectric layers metallic oxide, rendering their durability closer tothe durability of stacks using instead dielectric layers made of nitridelike silicon nitride. It seems that the gain in durability is stillhigher if Sb is chosen rather than Al in the composite oxide layer.

The invention may be used for glass substrates or any other transparentsubstrates, notably made of organic polymers as reminded in the preambleof the application.

The layers of the invention may be used as thin overcoat layer forprotection purpose, or as a “blocker” layer (this terl means that thelayer protects the functional layer, in metal like Ag, fromdeterioration due to the deposition of the following layer in metallixoxide by reactive sputtering in presence of oxygen), for example in athickness range of about 2 to 6 nm. The thickness may be greater, forinstance from 7 to 50 nm, if they are used to play a significant opticalrole.

The layers of the invention may be incorporated in many stacks of thin,interferential layers, notably in stacks having a functional layer withanti-solar properties or which is a low-emissive one, like Ag layer(s).The stack may contain one or several Ag layers, as described in EP 638528, EP 718 250, EP 844 219, EP 847 965, FR98/13249 and FR/98/13250. Thestack may also contain another kind of functional layer, for example inmetal like an Ni-Cr alloy or steel as described in EP 511 901, or innitride like TiN or ZrN.

The dielectric layer of the invention may be part of an anti-reflectingstack of layers, as descibed in EP 728 712 or WO 97/43224, or any otherstack of layers having a thermal, optical, electrical function and usinddielectric/oxide layers having a refractive index around 2.

The substrates may also be used to produce monolithic (a singnesubstrate), laminated or multipel glazings (double glazing, windshield .. . ). They may be mounted in buildings, in vehicles, for diplay panels. . .

As an illustration, herebelow some stacks of layers incorporating alayer according to the invention

Transparent substrate/SnO₂/ZnO/Ag/optional blocker, likeNiCr/SnO₂/ZnSnO:Al or Sb

Transparent substrate/SnO₂/ZnO/Ag/optional blocker like NiCr orTi/SnO₂/SiO₂/SnO₂/ZnSnO: Al or Sb

The stacks may contain two Ag layers.

To be underlined also that the amounts in added metal like Al or Sb inthe metallic target are approxilately the same ones as those in thelayers obtained from the target.

The stacks may of course contain several layers according to theinvention, notably a blocker one and an overcoat one.

We claim:
 1. In a layer stack for transparent substrates with at leastone metal oxide composite layer produced by reactive cathodic sputteringfrom a metallic alloy target containing Zn and Sn, the improvementwherein the metal oxide composite layer contains one or more of theelements Al, Ga, In, B, Y, La, Ge, Si, P, As, Sb, Bi, Ce, Ti, Zr, Nb andTa and has a thickness from about 2 to 6 nm.
 2. Layer stack according toclaim 1, wherein the amount of the elements Al, Ga, In, B, Y, La, Ge,Si, P, As, Sb, Bi, Ce, Ti, Zr, Nb and/or Ta in the metal oxide compositelayer relative to the total amount of metal is from 0.5% to 6.5% byweight.
 3. Layer stack according to claim 1, wherein the metal oxidecomposite layer contains from 35 to 70% by weight Zn and from 29 to64.5% by weight Sn, in each case relative to the total amount of metal.4. Layer stack according to claim 3, wherein the metal oxide compositelayer contains from 66 to 69% by weight Zn, from 29 to 32% Sn and from 1to 4% by weight Al or Sb.
 5. Layer stack according to claim 1, whereinthe metal oxide composite layer defines at least one of a lower and anupper antireflection layer of a layer stack having one or morefunctional layers made of a metal.
 6. Layer stack according to claim 1,wherein the metal oxide composite layer is a diffusion barrier layer ina multilayer stack.
 7. Layer stack according to claim 1, wherein themetal oxide composite layer is a sublayer of at least one of a lower andan upper antireflection layer.
 8. Layer stack according to claim 7,having a layer sequence of substrate—SnO₂—Me—Ag—Me—SnO₂—Zn_(x)Sn_(y)Al_(z)O_(n), wherein Me defines ablocker metal or blocker metal alloy.
 9. Layer stack according to claim7, having a layer sequence of substrate—SnO₂—Me—Ag—Me—Zn_(x)Sn_(y)Al_(z)O_(n)—SnO₂, wherein Me is a metal ormetal oxide comprising Ti, Ta, Zr or CrNi.
 10. Layer stack according toclaim 1, having the sequence SnO2/ZnO/Ag/optional blocker/SnO2/ZnSnO:Alor Sb or the sequence SnO2/ZnO/Ag/optionalblocker/SnO2/SiO2/SnO2/ZnSnO:Al or Sb.
 11. Layer stack according toclaim 1, wherein the stack further comprises at least a metal, metalalloy, or metal nitride functional layer.
 12. Layer stack according toclaim 1, wherein the stack has an anti-solar, low emissivity antireflecting or electrical function.
 13. Layer stack according to claim 1,wherein the composite layer has a spinelle structure.
 14. Transparentsubstrate in glass or polymeric material, rigid or flexible, coated onat least one of its faces by a stack of layers according to claim
 1. 15.Monolithic, laminated or multiple glazing incorporating the transparentsubstrate according to claim
 14. 16. Process for producing a stack oflayers for transparent substrates with at least one metal oxidecomposite layer of a metallic alloy containing Zn and Sn, wherein themetal oxide composite layer contains one or more of the elements Al, Ga,In, B, Y, La, Ge, Si, P, As, Sb, Bi, Ce, Ti, Zr, Nb and Ta and whereinthe composite layer is deposited to a thickness from about 2 to 6 nm byreactive sputtering from a metallic target which contains Zn, Sn and atleast one of the following elements: Al, Ga, In, B, Y, La, Ge, Si, P,As, Sb, Bi, Ce, Ti, Zr, Nb, and Ta.
 17. Layer stack according to claim5, wherein at least one of the one or more functional layers is a silverlayer.
 18. Layer stack according to claim 6, further comprising at leastone metal, metal alloy, or metal nitride functional layer.
 19. Layerstack according to claim 7, further comprising at least one metal, metalalloy, or metal nitride functional layer.
 20. Layer stack according toclaim 18, wherein the metal oxide composite layer has a spinellestructure.
 21. Layer stack according to claim 19, wherein the metaloxide composite layer has a spinelle structure.
 22. Layer stackaccording to claim 18, wherein the one or more elements comprises Al,Sb, or both.
 23. Layer stack according to claim 19, wherein the one ormore elements comprises Al, Sb, or both.
 24. Layer stack according toclaim 22, wherein the at least one functional layer comprises a silverlayer.
 25. Layer stack according to claim 23, wherein the at least onefunctional layer comprises a silver layer.
 26. Layer stack according toclaim 1, wherein the metal oxide composite layer does not containhydrogen or fluorine.